底泥污染質釋放問題一直攸關著水質的優劣，底泥本身即為一多孔介質，內部存在大量污染源，雖然底泥也為多孔體，但由於其孔隙微小的特性，污染物釋出實為緩慢，以往有研究希望藉由導入擁有孔隙較大之孔隙介質來加速底泥污染物的釋出，經前人研究證實此方法確有其效，且加入流速的考量時，污染質釋出的通量隨流速增加而增大。

本文主要目的在於利用可視化方法，了解應用孔隙介質增加河床底泥污染質加速釋放之現象，實驗以色素當作孔隙介質內部污染質，藉由不同性質之孔隙材料搭配上層水體之流速變化情況，闡明上層水體流速與孔隙結構之改變對污染質移動之影響。

水流流經孔隙介質時，由於水流入侵作用使孔隙介質內部流體產生流動現象，污染質在水流的帶動之下加快了移動機制。經實驗現象發現水流入侵所造成之擾流區與孔隙介質有關，孔隙介質的孔隙與寬度影響著擾流區深度Ypt，擾流區深度隨著孔隙斷面加大及砂孔寬度增加而加深，另一方面，上層水體的流速也是影響擾流深度的因素，底泥上層水體流速增加將加深了擾流深度。

Contaminants release from mud bed will influence water quality. The mud bed could consider as a porous medium existing a great deal of contaminants inside, but contaminant release is slowly due to the characteristics of mud bed structure. Former researches hoped to accelerate contaminants release from mud bed by using sand drain system to change the porous structure of mud bed. This method had verified experimentally. The experiments consider the flow dynamics, results showed the contaminants flux increasing accompanied with water velocity increasing.

The purpose of this paper was understood what the mechanisms of application of sand drain system to influence the contaminants releasing. The experiments conducted in a flume. Red dye was used to present the contaminants in porous materials. The porous materials and water velocity were changed.

Results showed fluid inside porous materials were produced to move by the intrusion of upper water flow, that would push dye forward and accelerating it’s moving. Through experimental observations could be found the depths of disturbed zone by intrusion were related to porous materials. The void scale and width of sand drain system influenced the depths of disturbed zone, depths increased with the void scale or width of sand drain system increased. Furthermore, the increasing of water velocity would deepen the depths of disturbed zone. The depths of disturbed zone increasing would increase the dye moving velocity in the porous materials.

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